1. Field of the Invention
The present invention relates to a throttle valve control system for regulating a valve opening ratio of the throttle valve employed in an engine of automobile and the like, more particularly to the throttle valve control device for controlling the throttle valve electrically and remotely in response to a depression ratio of an accelerator pedal to be depressed.
2. Description of the Prior Art
An automobile and the like generally control an engine output by regulating an air-fuel ratio to be introduced into a suction passage of the engine in the manner that the throttle valve positioned in the suction passage of the engine is open or closed to thereby vary the area of the suction passage. The throttle valve is operated to be open or closed with interlocking with the depression ratio of the acceleration pedal.
A prior art throttle valve control system is generally structured that acceleration of the accelerator pedal is delivered to the throttle valve via a mechanical means such as link or wire.
However, there are proposed various throttle valve control system having such an arrangement that the throttle valve is controlled electrically and remotely in response to the depression ratio of the accelerator pedal.
A typical prior art throttle valve control system is disclosed in Japanese Patent Laid-Open Publication No. 58-13135 and will be described herewith with reference to FIG. 4.
A throttle valve 31 is driven by a DC motor 32 to thereby be open or closed. More in detail, a rotation of the DC motor 32 is controlled by a motor driver 37 in the manner that an output signal from the valve opening ratio detector 33 for detecting the valve opening ratio of the throttle valve 31 and an output signal from a depression rateio detector 35 for detecting the depression ratio of the accelerator pedal are supplied to a comparator 36 where both the signals are compared with each other on the basis of a predetermined accelerator pedal operation/throttle valve operation characteristic which is stored in the comparator 36 to decide an appropriate valve opening ratio of the throttle valve, and an output signal from the comparator 36 is supplied to a motor drive 37 which amplifies the output signal from the comparator 36 and supplies it to the DC motor 32 for controlling rotation of the DC motor 32. The throttle valve 31 is urged by a return spring 38 in the direction to be closed which is provided for preventing the throttle valve 31 from flapping due to negative pressure caused by the suction air for thereby effecting a stable control of the throttle valve.
The DC motor 32 requires a torque greater than the urging force of the return spring for stably controlling the throttle valve 31 as well as closing the throttle valve. However, since the DC motor 32 runs generally in high speed with small torque, a reduction mechanism such as reduction gear and the like is required to be intervened between the DC motor 32 and a rotary shaft 39 of the throttle valve 31.
An ultrasonic motor having piezoelectric element is known and disclosed in Japanese Patent Laid-Open Publication No. 53-14682. The ultrasonic motor is small in size, light in weight and has a characteristic that it runs at high speed with large torque and a superior response characteristic.
However, there are following problems in the prior art electric throttle valve control system.
First, throttle valve conrol system is complex and large in size since the throttle valve 31 and the DC motor are connected via a reduction mechanism 40.
Secondly, the DC motor 32 is slow in starting of rpm thereof and inferior in the response characteristic.
Thirdly, when the current is stopped to be supplied to the DC motor 32 which is deenergized due to an urgent trouble the throttle valve shall be closed in failsafe point of view. However, there is a problem that the throttle valve is fixedly positioned while it is open due to a load applied thereto by the DC motor 32 and a reduction mechanism when the throttle valve 31 msut be returned to a close state by the return spring 38.